1. Field of Endeavor
The invention relates to the reduction of emissions from an annular combustor of a gas turbine plant. More specifically, the invention relates to a method of reducing emissions from premix burners used in the high-pressure combustor of a gas turbine plant with sequential combustors.
2. Definitions
In particular, throughout this specification a gas turbine plant is taken to mean and is defined as a gas turbine plant shown in FIG. 1 and described as follows. The first element of the gas turbine plant is a compressor 21 for compressing air for use in a high-pressure combustion chamber 22 fitted with premix burners 20 and also for cooling. Partially combusted air from the high-pressure combustor 22 passes through a high-pressure turbine 23 before flowing further into a low-pressure combustion chamber 24 where combustion occurs by self-ignition. In this chamber fuel is added to unburnt air from the first combustor 12 via a lance 37. The hot combustion gases then pass through a lower pressure turbine 25 before passing through a heat recovery steam generator. In order to generate electricity, the compressor 21 and turbines 23, 25 drive a generator 26 via a shaft 30
Further, throughout this specification a pre-mix burner is taken to mean and is defined as a burner, as shown in FIG. 2, suitable for use in the high-pressure combustor of a gas turbine plant. More specifically, it includes a conical swirl shaped body in the form of a double cone 11, which is concentric with a burner axis surrounded by a swirl space 17. A central fuel lance 12 lies within the burner axis extending into the swirl space 17 to form the tip of the swirl body 11. In a first stage 18, pre-mix fuel is injected radially into the swirl space 17 through injection holes in the fuel lance 12. In a second stage 14, pre-mix fuel is injected through injection holes located in the double cone 11 section of the burner into an air stream conducted within the double cone 11.
3. Brief Description of the Related Art
Combustion chamber dynamics of gas turbine plants with annular ring combustors not having canned burners are generally dominated by circumferential pressure pulsation. There are many supplementary causes for the pulsation, including the velocity of the fuel/air mixture through the burner, where the higher the velocity the greater the pulsation potential. In contrast to the negative effect of increased burner gas velocity, increasing velocity reduces NOx and for this reason alone there is a need to have alternative methods that enable higher burner gas velocity operation. Further as older plants are general poorer performing than newer plants, the desire to improve the emission performance of older plants is particularly high.
A method of ameliorating the detrimental effects preventing higher burner velocity operation is by disruption of burner configurational spatial uniformity. For example, DE 43 36 096 describes an arrangement where burners are displaced longitudinally in relation to each other, while WO 98/12479 discloses a burner arrangement where burners of different sizes are used as a means of stabilizing the flame.
While for new designs such configurations can easily be configured, the opportunity to change the burner layout in a preconfigured combustor is limited and, as a result, the above layouts cannot be suitably applied to preconfigured combustors. U.S. Pat. No. 6,430,930, disclosing an arrangement having burners with varying characteristic shapes along the longitudinal direction, as well as a secondary feature in the radial plane, is similarly unsuitable as suitably significant disruption of the spatial uniformity of burners cannot be achieved such that significant burner velocity change can be realized without redesigning of the combustor chamber.
Despite the unsuitability of known methods, there remains a need to reduce the emissions of existing gas turbine plants by solutions that do not require major modification involving changing the size of the combustor.